A file photo of the Army Public School in Peshawar a day after the terrorist attack on Dec. 16 in 2014

The hangings were the first executions of civilians convicted by Pakistan’s military courts, which were set up after the massacre through a constitutional amendment.

The executions were confirmed by three security sources, two of whom are based in Kohat, where the men were hanged early in the morning at the city’s civilian-run central jail.

Hazrat Ali, Mujeeb ur Rehman, Sabeel and Abdus Salam had been convicted on August 13, according to a military statement sent on that date. All were identified as members of the Toheedwal Jihad Group (TWG), a previously unheard of faction of the Pakistani Taliban.

Three others were also sentenced to death for involvement in the attack, according to the same military statement, but death warrants have not yet been issued for them.

All nine attackers were killed in the siege on Peshawar’s Army Public School, which killed 151 people on Dec. 16, 2014. It was the worst Taliban attack on Pakistani soil.